Various publications, including patents, published applications, technical articles and scholarly articles are cited throughout the specification. Each of these cited publications is incorporated by reference herein, in its entirety. Full citations for publications referenced by numbers in parentheses or otherwise not cited fully within the specification are set forth at the end of the specification.
Cytomegalovirus (CMV) is a herpes virus classified as being a member of the beta subfamily of herpesviridae. According to the Centers for Disease Control and Prevention. CMV infection is found fairly ubiquitously in the human population, with an estimated 40-80% of the United States adult population infected. The virus is spread primarily through bodily fluids, and is frequently passed from pregnant mothers to the fetus or newborn. In most individuals. CMV infection is latent, although virus activation can result in high fever, chills, fatigue, headaches, nausea, and splenomegaly.
Although most human CMV infections are asymptomatic. CMV infections in immunologically immature or immunocompromised individuals, such as newborns, HIV-positive patients, allogeneic transplant patients and cancer patients, can be particularly problematic. CMV infection in such individuals can cause severe morbidity, including pneumonia, hepatitis, encephalitis, colitis, uveitis, retinitis, blindness, and neuropathy, among other deleterious conditions. In addition, CMV is a leading cause of birth defects. At present, there is no cure or preventive vaccine for CMV infection.
The entry of herpesviruses into cells is a complex process initiated by adsorption and receptor binding and followed by fusion of the virus envelope with a cell membrane. Fusion occurs at either the plasma membrane or an endosomal membrane. For instance, Epstein Barr virus (EBV) enters primary B cells via receptor-mediated endocytosis (1, 2), yet it infects epithelial cells or transformed B cells by fusion of the virion envelope with the plasma membrane (1). Herpes simplex virus fuses with the plasma membrane of some cell types, but enters others by endocytosis (3-6). Human cytomegalovirus (HCMV) infects multiple cell types in vivo, including epithelial cells, endothelial cells and fibroblasts (7). It fuses with the plasma membranes of fibroblasts (8), but enters retinal pigmented epithelial cells and umbilical vein endothelial cells via endocytosis (9, 10).
The mechanism by which herpes viruses ‘choose’ their route of entry remains unclear. It is generally assumed that entry pathways are mainly determined by the host cell, but there is precedent for tropic roles of virion glycoproteins (11). EBV virions contain two gH complexes, gH/gL and gH/gL/gp42 (12, 13), which have mutually exclusive functions (11). Fusion with the plasma membrane of B cells is mediated by gH/gL/gp42 (14-16), but entry into epithelial cells is triggered by gH/gL (11, 12, 17). The cell type in which EBV is produced can alter its tropism. B-cell-derived EBV virions contain less gH-gL-gp42 than epithelial-cell-derived virions. As a result. B-cell-generated virus is more infectious for an epithelial cell and epithelial cell-derived virus is B cell tropic (18).
HCMV also encodes two gH/gL complexes: gH/gL/gO and gH/gL/pUL128/pUL130/pUL131 (19, 20). The gO-containing complex is sufficient for fibroblast infection, whereas the pUL128/pUL130/pUL131-containing complex is required to infect endothelial and epithelial cells (19-21). The AD169 laboratory strain contains only the gH/gL/gO complex in its virions (19). The absence of the second gH/gL complex is responsible for the loss of epithelial and endothelial cell tropism in HCMV laboratory strains (19-22).
There is a need for variety and diversity of CMV vaccines, and for effective means to control the spread and activation of the virus, particularly in immunocompromised individuals and pregnant women. The present invention addresses that need.